As shown in FIG. 1, a cellular wireless communication system is mainly composed of Core Network (CN), Radio Access Network (RAN), and terminals. Core Network is responsible for non-access stratum transaction, for instance, the updating of the location of a terminal, and is the anchor of user plane. RAN comprises eNB, or eNB and eNB controller, and the RAN is responsible for access stratum transaction (for instance, the management of radio resources), there can be a physical and logical connection between eNBs, such as the connection between eNB 1 and eNB 2 or eNB 3 as shown in FIG. 1, and each eNB can connect to one or more CN nodes. The terminal, i.e. User Equipment (UE), refers to various equipments which can communicate with cellular wireless communication network, for example, mobile phone or laptop, etc.
In cellular wireless communication system, the wireless coverage of fixed eNB network is limited because of various reasons, for example, various kinds of building constructions blocking the radio signal causes the inevitable coverage leak in the coverage of wireless network. In addition, in the marginal area of a cell, the weakening of radio signal intensity and the interference of the neighboring cell result in the poor quality of communication and the increasing of the error rate of wireless transmission when the terminals are in the marginal area of the cell. In order to increase throughput of data transmission, group mobility, temporary network deployment, throughput of the marginal area of the cell and coverage of a new area, a solution is to introduce a wireless network node, which is called relay, into the cellular wireless communication system. As shown in FIG. 2, Relay is the station which has the function of communicating data and possible control information through wireless link between the other network nodes, also called Relay Node/Relay Station. UE directly served by eNB is called Macro UE, UE served by Relay is called Relay UE.
The definition of the interfaces between all network elements is as follows:
direct link: the wireless link between eNB and Macro UE comprises downlink/uplink(DL/UL) direct link, called Uu interface.
access link: the link between Relay and Relay UE, comprising DL/UL access link, also being Uu interface.
backhaul link: the wireless link between eNB and Relay, comprising DL/UL relay link, called Un interface.
UE cannot distinguish the cells under the control of the Relay and the fixed eNB, from the view of UE, the cell under the direct control of eNB (called ordinary cell) does not have differences from the cell under the control of the Relay (called relay cell). Relay cell has its own Physical Cell Identifier (PCI), and sends the broadcast like a ordinary cell does, when UE stays in the relay cell, the relay cell can assign and schedule wireless resources to UE by itself, can be independent of the scheduling of wireless resources of eNB involved the relaying, the eNB involved the relaying is called Donor eNB, i.e. the eNB which is connected to Relay by backhaul link. The interface and protocol stack between relay cell and relay UE are the same as those between ordinary cell and Macro UE.
Long Term Evolution-based (LTE) cellular wireless communication system can adopt the flat structure based on Internet Protocol (IP). As shown in FIG. 3, LTE cellular wireless communication system is composed of Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and CN node. Wherein CN node comprises mobility management Entity (MME), servicing gateway (S-GW). MME is responsible for the work related to the control plane, for example, the mobility management, the processing of non access stratum signaling, the management of mobility management context of user, etc; S-GW is responsible for the transportation, forwarding and routing handover of UE user plane data and so on. E-UTRAN comprises eNB, the eNBs are inter-connected through X2 interface logically, which is used for supporting the mobility of UE in the whole network to ensure the seamless handover.
Each eNB is connected to system architecture evolution (SAE) CN through S1 interface, S1 interface supports the multipoint connection between eNB and MME, S-GW, eNB is connected to MME through control plane S1-MME interface. S1-MME interface protocol stack is shown in FIG. 4; its network layer adopts IP, the transmission layer above the network layer uses stream control transmission protocol (SCTP), the top application layer (i.e. control plane) uses the transmission bearer of the bottom layer to transmit the signaling of S1-AP.
each eNB is connected to S-GW through user plane S1-U interface, the interface protocol stack of S1-U is shown in FIG. 5, the transmission bearer is composed of GTP-U/UDP/IP, and is used for transmitting the user plane protocol data unit (PDU) between eNB and S-GW. The Tunnel Endpoint Identifier (TEID) of GTP-U and the IP address identifier transmission bearer comprise: source GTP-U TEID, destination GTP-U TEID, source IP address and destination IP address, wherein, the UDP port number is fixed as 2152, while GTP-U is a tunnel protocol for seamless transmission of IPv4 and IPv6. Each transmission bearer is used for bearing Service Data Flows.
Each eNB transmits signaling and data with UE through Uu interface (which is originally defined as the wireless interface between UTRAN and UE). FIG. 6 and FIG. 7 show the air interface protocol stack between eNB and UE from the user plane and the control plane. The user plane from top to down is Physical Layer (PHY), Medium Link Control (MAC), Radio Link Control (RLC) and Packet Data Convergence Protocol (PDCP) respectively. Above the lowest lay (i.e. the physical lay), MAC is responsible for the mapping from the logical channel to the transmission channel and the process of multiplexing/demultiplexing the data, the scheduling of physical resource of the bottom layer, and hybrid ARQ of data packet, etc. RLC layer ensures the data to be transmitted reliably and orderly, and finishes the process of multiplexing/demultiplexing the upper layer data packet by the method of ARQ and so on. PDCP layer is responsible for the header compression of IP data packet, and the encrypting/decrypting and the integrity protection of the data packet and etc. The control plane uses the bearing of user plane, which is called Radio Bearer in Uu interface, to transmit the signaling of the control plane, i.e. the signaling of RRC layer. RRC layer and the all the layers below it are called Access Stratum, finishing the access bearer between UE and access network, and after accessing, the access stratum can bear the signaling of Non Access Stratum (NAS).
MAC/RLC/PDCP protocol layer works as shown in FIG. 8, wherein the Scheduling/Priority Handling module of MAC layer mainly multiplexes the Service Data Units (SDU) from one or more logical channels to the Transport Blocks (TB) of the transmission channel. MAC chooses scheduling resources according to the Quality of Service (QoS) of the service transmission on the logical channel. The specific parameters of QoS are composed of QoS class identifier (QCI), Allocation and Retention Priority (ARP), Guaranteed Bit Rate (GBR) and Maximum Bit Rate (MBR). QCI identifies a set of standard QoS parameters, including priority, Packet Delay Budget (PDB) and Packet Error Loss Rate. Most of QoS parameters need to be guaranteed by scheduling priority processing module of MAC. The PDU format of MAC is shown in FIG. 9, the PDU is composed of MAC header and MAC load, MAC header is composed of a number of MAC sub-headers, the transmission content at the corresponding location of each sub-header identifier in MAC load can be MAC Control Element (CE) or SDU coming from logical channel. There are 3 types of Sub-header, as shown in FIG. 10, wherein E indicates whether there is a sub-header after the present MAC sub-header, if there is no sub-header, then the following is MAC load. For SDU in the MAC load, the Logical Channel Identifier (LCID) carried in the sub-header identifies the logical channel which the SDU comes from, and L identifies the length of this SDU.
The different service flows of UE have different QoSs, the different QoS services between UE and Packet Gateway (termed as PGW) are borne by the different Evolved Packet System bearer (EPS bearer), In the access network system of LTE, EPS bearer is borne by the bearer service unit of E-UTRAN Radio Access Bearer (E-RAB). In LTE system, E-RAB bears with two sections, one is Radio Bearer between UE and eNB, the other is S1 Bearer between eNB and S-GW. The transmission borne by both these two sections satisfies the QoS requirement of E-RAB. For the radio bearer on Uu, the QoS of one E-RAB is guaranteed by the scheduling/priority handling module of MAC, for example, the GBR requirement of E-RAB make MAC guarantees that the data rate of E-RAB is not lower than GBR when scheduling. In addition, for example, the requirement of Packet Delay Budget in QCI requires that 98% of the data should be transmitted in the time defined by PDB, so MAC needs to satisfy the requirement of PDB when scheduling.
In the scene of including a Relay, on Un interface, a single connection is established between the Relay and the Donor eNB, all services of all UEs of this Relay will be borne on this connection. The scheduling for the original service of UE can only satisfy the scheduling requirement of UE, for the Relay which carries a large amount of UEs, the scheduling of these UEs will be combined to be a scheduling for one Relay. On Un interface, Relay which is configured as the scheduled entity cannot satisfy the QoS requirement of each service of UE of the Relay.